Last night I had a really weird dream. I dreamt that the students who made Narbacular Drop, the space-bending indie game I played last year, had been hired by Valve to make a beautiful new version in the Half-Life universe.
You played this wide-eyed girl with strange metal braces on her shins like Eli Vance's prosthetic leg, and a droning robotic voice kept saying sinister things that I found incredibly funny. Also my Year Nine maths teacher was there. And I was naked.
But you're probably here to read about Portal, Valve's first-person puzzle game about opening rifts in space to cross uncrossable obstacle courses. It's designed around one simple but mind-expanding idea: you can shoot a hole in any wall, and then another one somewhere else, and if you walk into one you'll come out of the other.
Fire them side by side and you'll walk straight back into the room you just left. Fire them on floor and ceiling and you'll fall through the same room at terminal velocity forever.
The Aperture Science Handheld Portal Device (let's face it, the portal gun) is your only weapon, but its brazenly impossible uses are endlessly fascinating to perform. The internal logic is flawless, but you somehow never grasp it entirely however hungrily your brain gropes. It is, I'm just starting to realise, abstractly kinky. Portal, honey, how can your physics be wrong when they feel so right?
The game grips you by the wrist and leads you briskly past the befuddling basics of these rifts, straight to the good stuff. Within a few short levels you're using orthogonal portals to translate your gravitational potential into lateral velocity and flinging yourself exhilaratingly over turrets and lethal slime.
By nudging you gently through rooms that cleverly lead your eye to the correct - yet patently impossible - solution, it swiftly teaches you a dazzling roster of lunatic tricks.
Portal is a magnificent puzzle game. The titillating wrongness of every solution and the wonky thinking required to get there make you feel like a space-folding genius, and yet you'll almost never get stuck.
Soon you've learnt so many weird ways of perverting the forces and spaces in any room that you can throw yourself through them, like a futuristic Prince of Persia with abilities more improbable and wondrous by far.
The solutions eventually become more gymnastic - opening new portals mid-fling and plummeting back through those you've previously opened with pinpoint precision. But by then you're ready, and performing deliciously counter-logical mental inversions at breakneck speed is something to be relished.
The atmosphere, meanwhile, grows thickly sinister. Your sing-song robot guide GLaDOS (you'll find out what it stands for) doesn't seem unduly invested in keeping you alive. Soon her own delusions creep into her instructions to you. "The weighted companion cube," she announces as you snatch up a box, "will not threaten to stab you and cannot, in fact, talk. If the weighted companion cube does talk, the Enrichment Centre urges you to disregard its advice."
But as her coldly voiced lines become more murderous and surreal, they also get funnier. The writing is effortlessly sharp throughout, and with its single inhuman character Portal taps a thick vein of black, absurdist humour that becomes the game's propulsive force. You'll play faster just to hear the next beautifully unhinged line.
The game escalates magnificently. The puzzles change nature, requiring your to beat the system with the tricks it taught you rather than jumping through hoops. And at the same time, the humour reaches fever pitch - GLaDOS becomes so brilliantly deranged that at times it's hard to control yourself for laughing.